Is Asbestos a Problem in India?

What is Asbestos?   Asbestos is a mineral that makes a great fiber. People use that fiber in lots of building materials, like insulation, paints, electric wiring, wall boards, and floor tiles. It might be all around us.    Should I Be Concerned?   When any of these materials break apart, …

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Is Asbestos in China a Problem?

Asbestos in China is a commonly used building material, and it may be more dangerous than formaldehyde. So why do so few people talk about asbestos in China? Contrast that with other pollutants. One day a few years ago, a Chinese friend of mine asked me about jiaquan (甲醛). “Huh?” I …

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Car Air Pollution Stopped Driving

Do We Need Car Air Purifiers? Do they Work?

Car air purifiers sound like a great idea. But do we need them? Do car air purifiers even work?  Soon after I started making DIYs, people emailed me asking if we could make an air purifier for their car. My initial reaction was, “Great idea!” On the highways, we’re surrounded …

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Shanghai Technical Inspection Bureau Mask Tests

It’s tough to get good mask data on a wide range of consumer masks. I’ve posted some of my own test data and test data from Dr. Saint Cyr. But another great source of even more mask tests comes from the Shanghai Municipal Bureau of Quality and Technical Supervision. I’ve linked to …

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Dylos DC1100

How Accurate Are Common Particle Counters?

When I started Smart Air in 2013, I wanted to buy an air quality monitor. I had basically two options. I could buy a US$260 Dylos or spend thousands of dollars on the crazy expensive particle counters. Since then, the market has exploded with new air quality monitors as cheap as …

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3m mask fit

How to Do a Mask Fit Test at Home: Poor Man’s Fit Test

Since mask fit-test machines cost $10,000, many people need a simpler, practical way to check that their mask is sealing properly on their face. This simple four-step “poor man’s fit test” will help people check the fit of their mask and find leaks. I was fortunate enough to visit 3M’s …

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Are DIY Purifiers Still Cheap in the Long Run?

When I published tests of the DIY compared to the expensive machines, a couple people on Zhihu (China’s Quora) asked if you really save money in the long run with the DIY once you calculate the cost of changing the HEPA. After all, the IQ Air HEPA costs 1,782 RMB, …

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Is a 30 RMB HEPA Reliable?

After I published directions for how to make your own purifier, people asked me: “Which HEPAs should I use? Is this one trustworthy?”

That’s the type of question that makes a nerd like me happy because it means we need to get more data. So I ordered HEPAs from every manufacturer I could find, and I tested them all. After all the testing was done, I found I could ship the HEPAs that worked best for 80 RMB, which was cheaper than the 110 RMB HEPAs I was buying–quality and price!

Can HEPAs be even Cheaper? 

Later I found HEPAs for 20 RMB wholesale. I was excited. If HEPAs are that cheap, we can make the DIY even cheaper!

But the test data was terrible. These HEPAs weren’t anywhere close to getting 99% of particles, so I passed on them. If didn’t want to use it in my home, why would I want to ship them to other people?

A 99.97% HEPA for 30 RMB?

Thus I wasn’t surprised a couple weeks ago when I saw a store on Taobao selling HEPAs for 30 RMB and claiming that my HEPAs are 暴利 (aggressively overpriced). They claim that their HEPAs get 99.97% of particles, and if that’s true, maybe these were the holy grail of HEPAs I was looking for all along!

So I ordered two online and put them to the test. The first shock was seeing that it doesn’t have a frame:


That makes it harder retain its shape, but it might still be effective without a frame, so I put it through the tests.

Air Outlet Test

First, I tested it by putting it on the Cannon and testing the air coming out of the HEPA with a Met One Aerocet 531S. (The Met One is useful because it has a pump to regulate airflow. In air outlet tests, the particle counter is sitting in a stream of air, so using a pump maintains constant readings.)


The results weren’t pretty. Smart Air HEPAs got over 99.9% of particles, but the 30 RMB HEPA was below 90%–far below their claim of 99.97%.

Air Speed

But particle effectiveness isn’t everything. A HEPA in the 80% range might work better if it has better air flow. In that case, maybe the HEPA could process the air more times and clean the room air as well as a real HEPA.

To test that possibility, I put each HEPA on the Cannon and used a tool to measure air speed (fancy name “anemometer”). I placed the anemometer on the HEPA at four locations (left, right, top, bottom) and took the average air speed.


Again, the results weren’t pretty. So not only was the 30 RMB HEPA getting far fewer particles, it was letting much less air through.


Quality HEPAs for 30 RMB are still a dream. They’re not useless, but using this 30 RMB HEPA would expose people to significantly more particles.

I still hold out hope that manufacturers will be able to innovate cheaper HEPAs without sacrificing quality, but I haven’t seen those HEPAs yet.

Is the Taobao Store Owner Being Dishonest? 

The 30 RMB HEPA store makes claims that their HEPAs get 99.97% of particles, and the data clearly contradicts that, so it’s tempting to think that they’re lying.

But are they? I don’t know what’s in their mind, but my guess is that they simply didn’t go through the hassle of buying a particle counter and testing the HEPAs. I suspect that half of what seems like dishonesty on Taobao is actually just sloppiness.

As usual, I’m posting the raw data below.

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Smart Air is a social enterprise that creates simple, no-nonsense air purifiers and provides free education to protect people’s health from the effects of air pollution. We are proud to be the only certified B-Corp dedicated to fighting air pollution.